In general, acrylic acid is produced by a two-stage oxidation reaction of undergoing catalytic reaction of propylene with oxygen in the presence of a catalyst to produce acrlolein and undergoing catalytic reaction of the resulting acrlolein with oxygen.
On the other hand, in the recent years, due to a price difference between propane and propylene and for the purpose of overcoming problems such as complexity in process involving the two-stage oxidation, a process for producing acrylic acid in one stage by using propane as a starting material is studied, and there have been made a number of proposals with respect to catalysts to be used therefor. As representative examples thereof, there are enumerated catalysts made of a composite metal oxide such as [V, P, Te] bases, [Mo, Te, V, Nb] bases, and [Mo, Sb, V, Nb] bases.
Recently, there have been filed some applications for patent with respect to improvements of the foregoing metal oxide catalysts. That is, JP-A-10-137585 discloses a process for producing a catalyst by mixing a reaction aqueous solution obtained by allowing a molybdenum compound, a vanadium compound and an antimony compound to react in an aqueous medium at 70° C. or higher with a niobium compound, evaporating to dryness the resulting mixture, and further calcining it at a high temperature.
JP-A-10-230164 describes that in heat treating the respective metal compounds in the aqueous medium described in the foregoing patent document, a gas containing molecular oxygen is introduced into the aqueous medium and that when the catalyst as produced in this process is used for vapor phase oxidation reaction of propane, the yield of acrylic acid is further enhanced.
Also, JP-A-11-285636 describes a method for adding hydrogen peroxide to a reaction liquid of the respective metal compounds under heating and reaction or a reaction liquid thereof after the reaction in the aqueous medium as described in the foregoing JP-A-10-137585 and JP-A-10-230164.
However, even in the case of using the catalysts as described in the foregoing patent documents, the yield of acrylic acid in a one-stage oxidation reaction of propane does not reach a practical level required in the acrylic acid production.
JP-A-11-226408 discloses a method for allowing a metal powder to react with an oxometalate of other element and using a reaction liquid having the metal powder substantially dissolved therein as a raw material in the production of a catalyst. In this method, it is described that for the purpose of accelerating the reaction of the metal powder having a small dissolution rate, heating is carried out over a long period of time and that an oxidizing agent is added. However, JP-A-11-226408 does not provide any description with respect to a grinding treatment of the metal powder.